The epithelium of the rabbit cornea has been shown to possess both absorptive Na plus and secretory Cl minus transport mechanisms which, together with passive permeability properties, can influence the hydration of the stroma. The details of these ionic mechanisms are being studied by means of electrophysiologic techniques, biochemical analysis, pharmacologic modification and anatomical studies to better understand the role of the mammalian corneal epithelium in the control of corneal transparency in both normal and pathologic situations.